Chemical vapor infiltration and chemical vapor deposition (CVI/CVD) are well-known processes for forming high-performance composite materials. In particular, CVI/CVD is a useful process for fabricating structural composites such as, for example, brake disks, combustors and turbine components.
In general, the term “chemical vapor infiltration” (CVI) includes deposition of a matrix within the pores of a substrate, and “chemical vapor deposition” (CVD) includes deposition of a surface coating on a substrate. However, as used herein, the term CVI/CVD is intended to refer generally to infiltration and deposition of a matrix on and/or within a substrate.
CVI/CVD generally involves passing a gas (e.g., methane, propane, etc.) comprising a reactant component (e.g., carbon) around and through a substrate. The reactant component deposits on and within the pores of the substrate to form a composite structure. When the substrate and reactant component both comprise carbon, for example, a carbon/carbon composite material is formed.
The term “composite structure”, as used herein, refers to a substrate treated using CVI/CVD to contain a solid residue dispersed on and/or in the substrate. In an exemplary embodiment, the composite structure may comprise a substrate made of carbon having a solid carbon residue dispersed within. This may be referred to as a carbon/carbon composite.
In some conventional CVI/CVD processes, several substrates are stacked within a densification process chamber (i.e., a furnace) in order to increase the number composite structures produced per batch. During the process, the parameters within the chamber (i.e., temperature, pressure and flow rate of the gas) are controlled and/or varied to facilitate the deposition of the matrix within the substrate and create the composite structures.
However, there are several disadvantages associated with such conventional systems and methods for performing CVI/CVD. For example, using conventional CVPCVD processes, the temperature and pressure gradients are likely to vary at different locations within the chamber. As such, the rate and amount of deposition of the matrix in the substrates is likely to vary based upon the location of the substrate within the chamber, creating non-uniform composite structures.
However, the exhaust systems of such CVI/CVD densification systems tend to be less efficient and often require more power to operate. Such systems typically result in the undesirable formation of soot on the substrates, as well as build-up of carbon residue within the chamber, often requiring shut down of the system for cleaning and maintenance.
As such, improved system and methods for performing CVI/CVD that increase uniformity of the composite structures and efficacy of the CVI/CVD process while allowing quick unloading and reloading of the process chamber are desired.